The present invention relates to devices for injecting, administering, infusing, dispensing or delivering substances, and to methods of making and using such devices. More particularly, it relates to an injection device for an injectable product, e.g. a liquid medicine such as insulin, a growth hormone or an osteoporosis preparation.
EP 1 351 732 B1 discloses an injection device comprising a casing in which a reservoir for an injectable product and a conveying piston are arranged. A piston rod is in a threaded engagement with the casing. The device also comprises: a dosing member which can be axially moved relative to the casing and the piston rod in a threaded engagement with the piston rod; an operating button which can be rotated relative to the casing but cannot be axially moved and which is connected to the dosing member, secured against rotating; a coupling member which is connected to the piston rod such that it can be axially moved but is secured against rotating and which forms a two-way slip coupling with the dosing member; and lastly, a spring member which charges the coupling member with an elasticity force and thus holds it in a coupling engagement with the dosing member. The slip coupling is designed as a rotational slip coupling comprising two toothed rings which are in a latching engagement with each other which can be released against the force of the spring member and which thus form the coupling engagement. The latching engagement can be released in both rotational directions against the force of the spring member, such that the dosage can be increased by rotating the dosing member in one dosing direction and decreased by rotational slip coupling it in an opposite, correcting direction. In a dual function, the spring member acts as a coupling spring which tenses the coupling member into the coupling engagement with the dosing member, and as a delivery spring whose spring tension is increased by increasing the dosage during setting and which advances the piston during delivery. In order to prevent the coupling from inadvertently slipping while the dosage is being set, the toothed rings in the coupling engagement must withstand the spring tension. The force which the user must apply in order to increase the dosage is correspondingly high.